The role of laser wavelength and pulse frequency in inactivation of Escherichia coli and Listeria monocytogenes

Ultra violet (UV) lasers have been used in food industry, medicine and dentistry to deactivate pathogenic bacteria of various types. The use of laser and other pulsed light systems for phototherapy and other microbial disinfections are based on spectral characteristics and configuration of the light source used. Here we explore the extent to which two pulsed laser parameters (wavelength and pulse frequency) affect deactivation of two pathogenic bacteria; Escherichia coli and Listeria monocytogenes. Three pulsed laser wavelengths, 1064nm and its 2nd and 3rd harmonics, were used to irradiate samples of E. coli at approximately same fluence. A 350nm continuous wave flash lamb, with output configuration close to that of the 3rd harmonic of the laser, was also used for the purpose of comparison. The result indicates that the log reductions for the laser wavelengths are higher (almost double) that of continuous wave light. When E. coli and L.monocytogenes samples were irradiated with the 3rd harmonic wavelength using three different pulse frequencies, the result shows higher deactivation at higher pulse frequency than at lower pulse frequency